The present application relates to a semiconductor structure and a method of forming the same. More particularly, the present application relates to a semiconductor structure that includes a carbon-doped silicon germanium alloy layer as a punch through stopper that is located above a strain relaxed silicon germanium alloy buffer layer.
Strain relaxed buffer (SRB) layers are needed for strained channel complementary metal oxide semiconductor (CMOS) devices. As an example, a silicon germanium alloy (i.e., SiGe) SRB layer is used for growing tensily strained silicon (Si) channels for n-channel field effect transistors (i.e., nFETs), and compressively strained germanium or high-germanium percentage SiGe channels for p-channel field effect transistors (i.e., pFETs).
One major problem with using a SiGe material is the fast diffusion of n-doped species used to form well implants for pFETs. Arsenic has a much higher diffusion rate in a SiGe alloy than in silicon, leading to unwanted lateral diffusion of arsenic into the p-well region and/or upward into the pFET channel region during thermal processing, destroying the devices. Phosphorus diffuses a little less, but the problem remains the same. There is thus a need in the semiconductor industry for a method and structure that obviates the problem of fast dopant diffusion within a substrate including a strain relaxed silicon germanium alloy buffer layer.